Deck 13: Nuclear Magnetic Resonance Spectroscopy

Question 1

If a molecule contains 4 elements of unsaturation and signals in the ¹H NMR spectrum between δ 7.0 and 8.0 ppm, what structural group is likely to be present?

A) a carbonyl group
B) an aromatic ring
C) a hydroxyl group
D) a cyclohexyl ring
E) a carbon-carbon triple bond

Answer 1

an aromatic ring

Question 2

Predict the number of signals expected (disregarding splitting) in the ¹H spectrum of m-xylene (1,3-dimethylbenzene).

Answer 2

4

Question 3

What are the relative integrations for the ¹H NMR signals for the following compound?

A) 3:1:2:2
B) 3:3:2
C) 3:1:4
D) 5:3

Answer 3

3:1:4

Question 4

How many nuclear spin states are allowed for the ¹H nucleus?

A) 1
B) 2
C) 3
D) 4
E) 10

Question 5

On a 90 MHz spectrometer, calculate the frequency at which a proton absorbs if it appears at 4.20 ppm.

Question 6

The protons marked H_a and H_b in the molecule below are ________.

A) chemically equivalent or homotopic
B) enantiotopic
C) diastereotopic
D) endotopic
E) none of the above

Question 7

________ is commonly used as an internal reference in NMR spectroscopy; its signal is assigned δ = 0 in ¹H and ¹³C NMR spectroscopy.

Question 8

Which of the following functional groups has the most deshielded proton and would be predicted to show an NMR signal that is the farthest downfield?

A) benzylic - H
B) allylic - H
C) aldehyde - H
D) aromatic - H
E) acetylenic - H

Question 9

What information does the intensity (integration) of a signal in the ¹H NMR spectrum give you?

A) how many different types of protons are present
B) the electronic structure of the molecule close to each type of proton
C) how many protons of each type are present
D) how many neighboring protons are present

Question 10

Calculate the magnetic field that corresponds to the proton resonance frequency of 300.00 MHz. The gyromagnetic ratio of the ¹H nucleus is

Question 11

Predict the number of signals expected (disregarding splitting) in the ¹H spectrum of o-chlorophenol (2-chlorophenol).

Question 12

The energy difference between the allowed spin states for an ¹H nucleus is ________ the strength of the external magnetic field in which it is placed.

A) independent of
B) directly proportional to
C) inversely proportional to
D) exponentially related to
E) logarithmically related to

Question 13

Which of the following reasons best explains why aromatic protons have a larger chemical shift than protons one carbon removed from a halogen?

A) An aromatic ring is more electron withdrawing than a halogen.
B) A halogen is more electron withdrawing than an aromatic ring.
C) Electron movement induces a magnetic field opposing the external field.
D) Electron movement induces a magnetic field reinforcing the external field.

Question 14

What three-word term is abbreviated NMR?

Question 15

Predict the number of signals expected (disregarding splitting) in the ¹H NMR spectrum of the compound shown below.

Question 16

Using a 60 MHz spectrometer, the protons in dichloromethane appear at 5.30 ppm. When the same sample is placed in a 100 MHz instrument, where does the signal appear?

A) 8.33
B) 5.30
C) 3.18
D) cannot be determined from information given

Question 17

¹H nuclei located near electronegative atoms tend to be ________ relative to ¹H nuclei which are not.

A) shielded
B) deshielded
C) resonanced
D) split
E) none of the above

Question 18

Predict the number of signals expected (disregarding splitting) in the ¹H spectrum of dibutyl ether.

Question 19

A nucleus with an ________ atomic number or an ________ mass number has a nuclear spin that can be observed by the NMR spectrometer.

A) even; odd
B) odd; even
C) odd; odd
D) even; even

Question 20

Predict the number of signals expected (disregarding splitting) in the ¹H NMR spectrum of the compound shown below.

Question 21

What ¹H NMR spectral data is expected for the compound shown?

A) 3.8 (1H, septet), 2.1 (3H, s), 1.0 (6H, d)
B) 3.8 (1H, septet), 3.3 (3H, s), 1.0 (6H, d)
C) 3.3 (3H, s), 2.6 (3H, septet), 1.0 (6H, d)
D) 2.6 (1H, septet), 2.1 (3H, s), 1.0 (6H, d)

Question 22

Predict the number of signals expected, their splitting, and their relative area in the ¹H NMR spectrum of (CH₃)₃CCHO.

Question 23

The protons labeled Ha in the structure below generally show up as a triplet, even through there are three neighboring protons. The coupling constant is approximately 7 Hz. What does this suggest about the size of the coupling constant for the aldehydic proton?

Question 24

Use the structure below to state the relationship between the indicated protons as equivalent, enantiotopic, diastereotopic, or unrelated.
H_a & H_b:
H_a & H_c:
H_b & H_c:

Question 25

The protons marked H_a and H_b in the molecule below are ________.

A) chemically equivalent
B) enantiotopic
C) diastereotopic
D) endotopic
E) none of the above

Question 26

Predict the number of signals expected (disregarding splitting) in the ¹H spectrum of 1,1-dimethylcyclobutane.

Question 27

A peak split into a doublet of triplets gave the following measurements in its splitting pattern. State the coupling constants (J values) for both the doublet and the triplet.

Question 28

The following splitting pattern represents one of the vinyl protons of styrene. Identify which proton is represented and list all the coupling constants (J values) for the splitting pattern.

Question 29

A compound (C₅H₈O) shows IR absorptions at 3600 and 3300 cm^-1. Its ¹H NMR spectrum contained singlets at
and 2.9 (broad) (ppm) in a ratio of 6:1:1. Name this compound.

Question 30

Label the different ¹H environments in the structure below a, b, c.... Then complete the table for each different type of proton. The first one is done for you as an example. (Note: there may be fewer than 7 different proton environments)
environments a b c d e f g
chemical shift
(+/- 0.5 ppm) 1.9
spin-spin splitting s

Question 31

Predict the number of signals expected, their splitting, and their relative area in the ¹H NMR spectrum of 2-methylpropane (isobutane).

Question 32

Describe the number of signals and their splitting in the ¹H NMR spectrum of (CH₃)₂CHOCH₃.

A) 3 signals: 2 doublets and a septet
B) 2 signals: a doublet and a septet
C) 3 signals: a doublet, a quartet, and a septet
D) 4 signals: 2 doublets, a singlet, and a septet
E) 3 signals: a singlet, a doublet, and a septet

Question 33

What is the relative area of each peak in a quartet spin-spin splitting pattern?

A) 1:2:1
B) 1:2:2:1
C) 1:1:1:1
D) 1:4:4:1
E) 1:3:3:1

Question 34

What is the expected multiplicity and relative ratio of the area of the peak for the protons labeled Ha?

A) singlet with relative area of 1
B) triplet with relative area of 1:1:1
C) triplet with relative area of 1:3:1
D) multiplet with relative area of 1:6:15:20:15:6:1

Question 35

Predict the number of signals expected, their splitting, and their relative area in the ¹H NMR spectrum of CH₃CH₂OCH₃.

Question 36

The protons marked H_a and H_b in the molecule below are ________.

A) chemically equivalent
B) enantiotopic
C) diastereotopic
D) endotopic
E) none of the above

Question 37

What compound exhibits only two signals in its ¹H NMR spectrum, a triplet and a quintet?

A) BrCH₂CH₂CH₂Br
B) BrCH₂CH₂CH₂Cl
C) (CH₃)₂CHCH(CH₃)₂
D) CH₃CH₂CH₂CH₃
E) (CH₃)₂CHOCH(CH₃)₂

Question 38

What is the relationships between Ha and Hb in the following structure?

A) homeotopic
B) enantiotopic
C) diastereotopic
D) none of the previous

Question 39

Why is carbon-hydrogen splitting not a major part of ¹H NMR spectra?

Question 40

What ¹H NMR spectral data is expected for the compound shown?

A) 3.8 (1H, septet), 2.1 (3H, s), 1.0 (6H, d)
B) 3.8 (1H, septet), 3.3 (3H, s), 1.0 (6H, d)
C) 3.3 (3H, s), 2.6 (3H, septet), 1.0 (6H, d)
D) 2.6 (1H, septet), 2.1 (3H, s), 1.0 (6H, d)

Question 41

You have a sample and its ¹H NMR spectrum. You know your sample contains O atoms but not N atoms, and you suspect that your sample may be an alcohol. What common spectroscopic technique might you use to confirm your suspicion?

Question 42

Draw a splitting tree to show the complex splitting pattern for the H_b proton. (J_cis = 10 Hz, trans = 15 Hz and J_gem = 2 Hz

Question 43

How might the proton spectrum of ultrapure dimethylamine, (CH₃)₂NH, differ from the spectrum of this compound to which D₂O has been added?

Question 44

Why is carbon-carbon splitting typically not seen in ¹³C NMR spectra?

Question 45

Which compound generates positive peaks for the carbonyl in both its DEPT-90 and DEPT-135 spectra?

A) CH₃CH₂CHO
B) CH₃CH₂COCH₃
C) CH₃CO₂CH₂CH₃
D) CH₃CH₂CONH₂
E) H₂CO

Question 46

Any process faster than ________ will be recorded as an average by NMR spectroscopy.

A) 0.0005 seconds
B) 0.1 seconds
C) 0.01 seconds
D) 0.001 seconds
E) 1 minute

Question 47

The chair form of cyclohexane has protons in two distinct environments, axial and equatorial. When the proton NMR of cyclohexane is run on a 100-MHz instrument at 23°C, only one signal for the compound is observed. Explain this apparent contradiction.

Question 48

What type of carbon environment does not generate a signal in the DEPT-90 spectrum and gives a negative signal in the DEPT-135 spectrum?

A) quaternary
B) methine
C) methylene
D) methyl
E) carbonyl

Question 49

How many peaks appear in the proton spin decoupled ¹³ C NMR spectrum of the compound below?

A) 2
B) 3
C) 4
D) 5
E) 6

Question 50

An NMR spectrometer that operates at a frequency of 60 MHz for ¹³C NMR spectra, operates at what frequency for ¹H NMR spectra?

A) 15 MHz
B) 30 MHz
C) 60 MHz
D) 120 MHz
E) 240 MHz

Question 51

The ¹H NMR spectrum of ethanol is acquired and the hydroxyl signal appears as a singlet instead of a triplet. Offer an explanation.

Question 52

What is the approximate chemical shift of an alkynyl carbon in ¹³C NMR spectroscopy?

A) 10 ppm
B) 30 ppm
C) 70 ppm
D) 120 ppm
E) 200 ppm

Question 53

Give one reason why ¹³C NMR is less sensitive than ¹H NMR.

Question 54

How many peaks appear in the proton spin decoupled ¹³ C NMR spectrum of the compound below?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 55

If a signal is observed in the 170 to 200 ppm range in a ¹³C NMR spectrum, what is the most likely type of functional group associated with that carbon atom?

A) carbonyl carbon
B) allylic carbon
C) aromatic carbon
D) carbon/carbon triple bond
E) carbon/carbon double bond

Question 56

Predict the number of signals expected in the proton spin decoupled ¹³C spectrum of cyclopentane.

Question 57

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of the compound shown below.

Question 58

What multiplicities are observed in the off-resonance decoupled ¹³C spectrum of 2,3-dimethyl-but-2-ene?

Question 59

What compound exhibits three singlets in its proton spin decoupled ¹³C NMR spectrum?

A) BrCH₂CH₂CH₂Br
B) BrCH₂CH₂CH₂Cl
C) (CH₃)₂CHCH(CH₃)₂
D) CH₃CH₂CH₂CH₃
E) (CH₃)₂CHOCH(CH₃)₂

Question 60

What type of carbon environment does not generate a signal in the DEPT-90 spectrum and gives a positive peak in the DEPT-135 spectrum?

A) quaternary
B) methine
C) methylene
D) methyl
E) carbonyl

Question 61

Draw the ¹H NMR spectrum for the following compound.

Question 62

How could you tell the difference between these two compounds with ¹H NMR?

Question 63

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of the compound shown below.

Question 64

Predict the number of distinct quartets expected in the off-resonance decoupled
spectrum of the compound shown below.

Question 65

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of the compound shown below.

Question 66

Predict the number of signals expected in the proton spin decoupled ¹³C spectrum of 3-hexanone, CH₃CH₂COCH₂CH₂CH₃.

Question 67

Which carbon signal shows up in the 0-50 ppm region of the proton spin decoupled ¹³C NMR spectrum?

A) A
B) B
C) C
D) D
E) both C and D

Question 68

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Question 69

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Question 70

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Question 71

Predict the number of distinct quartets expected in the off-resonance decoupled
spectrum of the compound shown below.

Question 72

Which carbon signal is furthest down field in a proton spin decoupled ¹³C NMR spectrum?

A) A
B) B
C) C
D) D

Question 73

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of p-diethylbenzene (1,4-diethylbenzene).

Question 74

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Question 75

Predict the number of signals expected in the proton spin decoupled ¹³C spectrum of
(1,3-dichlorobenzene).

Question 76

Predict the number of signals expected in the proton spin decoupled ¹³C spectrum of
(1,4-dibromobenzene).

Question 77

Predict the number of signals expected in the proton spin decoupled ¹³C NMR spectrum of o-diethylbenzene (1,2-diethylbenzene).

Question 78

Draw the ¹³C NMR spectrum for the following compound.

Question 79

How many peaks appear in the proton spin decoupled ¹³C NMR spectrum of the compound below?

Question 80

Predict the number of distinct quartets expected in the off-resonance decoupled
spectrum of the compound shown below.